The present invention relates to apparatus and methods for determining the optical parameters of a lens, and more particularly to a method and apparatus for automatically and objectively obtaining measurements of such parameters.
In the past, to determine the quality of ophthalmic lenses, manufacturers have had to rely upon testing devices which require a good deal of subjective determinations by the operator of the testing device. One such typical measuring instrument, which requires careful manipulation of the lens and continual subjective evaluations, is disclosed in U.S. Pat. No. 1,383,678 to Tillyer et al. Because of having to rely on the subjective evaluations of each operator, differences in the readings acquired from operator to operator are encountered. Further, a relatively long period of time is required for even experienced operators to make an accurate measurement. Consequently, in order to measure the large quantities of lenses encountered in a production environment, a large number of operators is required.
Various attempts have been proposed in the prior art to alleviate these difficulties. One such method illuminated a test lens with collimated light, while behind the lens was placed an opaque mask containing two small holes symmetrically placed with respect to the axis of the system. The mask selects two bundles of rays from the refracted bundle passing through the lens. After first determining the separation of these bundles at some point down stream, the lens power of the lens could be calculated given the geometry of the optical system. However, this method is only useful for testing lenses having only spherical power, and also utilizes a moving part, namely a rotating chopper wheel having a slit therein, to determine the separation of the bundles.
U.S. Pat. No. 3,880,525 discloses a lens measuring device without moving parts that relies on the effect of a lens upon at least three small bundles of light. An analysis of the direction and amount of displacement of the bundles permits the sphere, cylinder and axis of the lens to be calculated. However, the repeatability and accuracy of devices of this type, as well as other commercial lens measuring devices, is dependent upon the curvature uniformity and surface quality of the lens. Furthermore, this device could not be relied upon to detect isolated defects in the lenses.
It would be advantageous to devise a method and apparatus, utilizing no moving parts, which is capable of consistently and easily providing objective measurements of the optical properties of lenses, including the ability to detect isolated defects, if so desired.